1. Field of the Invention (Technical Field)
The present invention relates to measuring systems and more specifically to a method and apparatus for measuring a mortar muzzle exit velocity.
2. Background Art
This present invention solves the problem of providing accurate primary instrumentation for the measurement of the velocity of a projectile at the muzzle point of exit. Many variables affect muzzle velocity. Examples include, but are not limited to barrel wear, propellant temperature, unique propellant burn rate, and air density. While some of these variables can accurately be accounted for individually, when taken in total, it is most efficient to simply measure the muzzle velocity and apply a correction factor to all subsequent firings. Radar systems presently are used to analyze the ballistic path but do not provide an actual point of exit measurement. Other existing prior art methods comprise the use of various inductive, optical, fiber optic strain gauges, and RF injection to obtain the muzzle velocity of a non-specific barrel guided projectile. The inductive approach exhibits a characteristic reduced frequency response while optical and fiber optic systems are not suitable to the combat environment or are not practical for fielding. RF injection requires that the barrel be penetrated at multiple locations which violates the military standard for barrel structural integrity.
Most all approaches must start with the same premise of detecting the round over a measured distance and calculating a time period of travel to resolve velocity. These prior art systems include:
U.S. Pat. No. 6,590,386 discloses an optical type detector and is used to detect paint balls in paint ball guns; U.S. Pat. No. 6,644,111 describes the use of a fiber optic bragg grating as a strain gauge detector; U.S. Pat. No. 6,563,302 describes the use of a voltage coil for underwater detection; U.S. Pat. No. 6,498,476 describes the use of transparent break screens for underwater detection; U.S. Pat. No. 6,064,196 describes the use of inductive coils and a magnet mounted on the projectile body; U.S. Pat. No. 6,020,594 discloses the use of two optical IR light beam assemblies; U.S. Pat. No. 5,267,502 does not disclose a muzzle velocity measuring device, but describes a computational method for predicting muzzle velocity from past doppler radar measurements using a Kalman filter or neutral network; and U.S. Pat. No. 4,928,523 discloses the use of a microwave generator to propagate energy into the gun barrel through drilled holes and measure the phase shift relative to projectile travel inside the barrel.
Single back-biased Hall effect sensors with digital signal processing (DSP) have been widely used to detect angular position and rotational speed of motion in powered shaft driven machinery by means of a multi-toothed gear wheel. It is new and non-obvious to apply this close proximity detection technique to a high-speed projectile traveling in a linear path of motion with only one target position and two rather than one sensor for detection.
The present invention is a unique system that uses back-biased digital Hall effect integrated circuit sensors with pre-conditioned digital signal processing (DSP) to accurately produce a time over distance variant function of the projectile which can be digitally resolved into precise velocity coded hexadecimal data words in digital resolver/discriminator electronics and further interpreted by a computer software interface.